The advancement of modern technologies also brings noises to people's living environment, which invades into our daily lives, causing restlessness and irritability thus seriously deteriorating the living quality. Especially, in current crowded metropolitans, since buildings are densely constructed and sufficient buffering space may not be available among them, sounds coming from different sources, e.g., television speakers or people's talks of nearby neighbors, may become very annoying and unbearable. With improvement on the level of living, people are gradually paying more and more attention to the comfortableness in their environments, and sound insulation materials are now comprehensively accepted and applied at various locations, such as residences, offices, music classrooms or the like. It is known that acoustic boards can be utilized as a type of sound insulation materials, whose acoustic absorption feature has been the focus of people's incessant efforts so as to ameliorate and enhance their sound elimination effect based on better structural designs.
Moreover, it is also understood that, with acoustic boards having different diameters of hole and opening rates, the sound absorption effect thereof with regards to sounds of various frequencies may correspondingly differ. Typically, although the range of human auditory sense could cover a band of approximately 20 to 20 k Hz audio frequencies, acoustic frequencies exceeding 10 k Hz may already generate poor hearing responses for general people. Consequently, to fit into human auditory senses, the sounding range of general instruments may usually locate within a span of about 20 to 4000 Hz, and the researches of the Applicants are accordingly performed based on such a band, in which a common 3270 Hz is set as the high frequency test and 880 Hz as the low frequency test for typical hearing range, and their acoustic absorption rates under six different conditions within such two frequency ranges are summarized, as hereunder shown in Table 1:
TABLE 1A1B1B2B3C1C2Diameter of0.20.40.691.271.731Hole (mm)Opening1131031Rate (%)Acoustic0.9941790.8013670.3355240.0778320.2831990.376532AbsorptionRate(880 Hz)Acoustic0.9930130.6976530.3692860.0434960.2590280.099883AbsorptionRate(3,270 Hz)
From Table 1, it can be observed that, B3 has a larger diameter of hole and the highest opening rate, its acoustic absorption effect is obviously the worst in several different test conditions; B2, C1 both have higher opening rates and poorer acoustic absorption rates, but the acoustic absorption rate of B2 is still better than C1 due to its smaller diameter of hole; comparatively, A1, B1 both have smaller diameters of hole and lower opening rates, so the acoustic absorption rates thereof are significantly elevated, in particular A1 demonstrates the best acoustic absorption rate because of its smallest diameter of hole. Therefore, as the first critical factor, the opening of the acoustic board should be preferably less or equal to 0.04 mm2.
Meanwhile, to fabricate micro through-holes with commonly available technologies, people mostly utilize the mould of multiple sharp tapered bodies to press down or punch in order to generate the acoustically absorptive micro-orifices having a corresponding diameter of hole or cross-sectional area on acoustic board materials. Unfortunately, as the diameter of hole getting smaller, the manufacture costs for the mould of tapered bodies may greatly soar, and, regarding to acoustically absorptive plate materials of higher hardness in particular, the mould may not be durable enough for long-term use, quickly worn off or even broken up, resulting in significant mould replacement costs. Moreover, it should be noticed that, upon pressing and piercing the acoustically absorptive plate materials with the tapered bodies, the sharper the tapered structure is, the more frequently burr structures may be created on the lateral side of the holes punched in the acoustic board, and such acoustically absorptive micro-orifices are so fine and tiny that subsequent modification or trimming operations may be very challenging; besides, these burr structures may also negatively influence the intended acoustic absorption effect thus reducing the yield of products. In addition, this machining approach may also further restrict the selections of available acoustically absorptive plate materials; i.e., thicker or harder decorative materials may have to be excluded from applicable options.
In prior art, some manufacturers considered to utilize plastic injection-molded technology to make acoustic boards; however, the design and fabrication for plastic injection moulds need to be configured depending on injection conditions, which means that the finer the acoustically absorptive micro-orifices are, the more delicate the moulds need to be, leading to higher difficulty in mould fabrication; and also, the mould stripping operation may cause damages to products, thus resulting in lowered product yield, increased costs, as well as undesirable restrictions to massive production.
Consequently, the present invention attempts to provide an acoustic board having displaced and passably abutted multiple through-holes, in which the piercing process needs not to be limited to conventional delicate moulds, but capable of applying moulds having greater diameters of hole for tooling operations, and then using a displacement process to allow the through-holes to be passably abutted thereby forming the intended acoustically absorptive micro-orifices. In this way, it is not only possible to lessen the abrasions in the moulds and reduce the costs, but eliminate burr structures potentially generated after the through-hole machining process; moreover, even slight burrs do appear, this issue may be easier to be resolved since the through-holes are wider, thus allowing the acoustic absorption effect thereof not to be affected by such burr issues on the acoustically absorptive micro-orifices.
Furthermore, it is also possible to apply the plastic injection technologies to allow the two moulds to be displaced and closely abutted such that the melted plastic gel may not easily leak in, thus successfully forming the acoustic holes of arbitrarily variable sizes; in this fashion, the mould of fine diameter may not break up upon mould stripping so as to reduce the mould manufacture costs, lower unnecessary mould losses and improve the yield of products.